<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        /* 
            控制台输出 console.log()
            弹窗输出 alert()
            页面输出 document.write()
        */
        let name;
        name = "jack";
        console.log(name);
        alert(name);
        document.write(name);
    </script>
</body>
</html>